The invention primarily relates to a series hydraulic hybrid transmission system, in particular for automotive vehicles. More specifically, the invention relates to a series hydraulic hybrid transmission system including a hydraulic circuit, an accumulator assembly in fluid communication with the hydraulic circuit and a control unit for controlling the system. The invention further relates to a method of controlling the series hydraulic hybrid transmission system. Hydraulic hybrid transmission systems of this sort may find application in off-highway working machines used in agriculture, mining or construction, such as tractors, wheel loaders, wheeled excavators, backhoe loaders, telehandlers, dumpers, or the like.
Hydraulic hybrid transmission systems including a hydraulic circuit and one or more hydraulic accumulators for hydraulic energy storage are a known technology. Hydraulic energy recuperated by the accumulators may be re-injected in the system to replace or supplement a primary energy source, for example an internal combustion engine.
However, the fuel consumption and performance of a hydraulic hybrid transmission system depend to a great extent on the control strategy used for operating the vehicle and have remained a challenge for developers.